The invention relates in general terms to the field of robotics, where jacks are used for bringing about reciprocal movement of the articulated elements or for the linear displacement of charges or loads, such as the arms or limbs of a robot. A first main application is for autonomous robots of the walking type or the type having a dynamically controlled suspension. The invention more specifically relates to an electric jack with a rotation-translation movement conversion system and with energy recovery, e.g. of the ball nut-screw type.